The response of adult volunteers to a series of ts or cold-adapted recombinants was evaluated. The A/Alaska/77-ts-lA2 (H3N2) and A/HK/123/77-ts-lA2 (HINI) viruses, each of which had a 37 degrees C shutoff temperature, were satisfactorily attenuated and induced an immunological response in greater than 84% of the volunteers. Virus shed by each of the volunteers retained the ts phenotype. A/Alaska/77 (H3N2) cold-adapted recombinant virus which possessed a 39 degrees C shutoff temperature for plaque formation was also suitably attenuated and immunogenic in volunteers. The A/HK/77 cold-adpated recombinant possessed a 37 degrees C shutoff temperature and was satisfactorily attenuated and immunogenic in volunteers. The virus shed by volunteers retained the ts and cold-adapted properties. These studies indicate that the two master strains of influenza A virus can confer, via the mechanism of gene transfer a satisfactory level of attenuation, immunogenicity, and genetic stability on virulent viruses belonging to two influenza A subtypes.